Of course, any previous convictions do not excuse his ‘horrific’ mistreatment by the airline, which the CEO has now apologised for.

However, they have become the focus of sustained media attention after a local paper brought to light the medic’s troubled past of illicit gay sex with a patient and previous positive tests for drugs.

According to official documents, in 2005 the Vietnamese-born medic was charged with 99 felony drug counts for illegally prescribing and trafficking painkillers and fraudulently filling prescriptions for hydocodone, Oxycontin and Percocet.

Video of what happened has been shared thousands of times, with people incredulous to see the 69-year-old being forcibly removed from the plane and bleeding heavily at the time.

In a statement, United Airlines said: ‘Flight 3411 from Chicago to Louisville was overbooked. After our team looked for volunteers, one customer refused to leave the aircraft voluntarily and law enforcement was asked to come to the gate.

‘We apologise for the overbook situation. Further details on the removed customer should be directed to authorities.’